ABSTRACT Early developmentally-based behavioral intervention has well-established positive effects and is recommended as the standard of care to support early brain maturation, health, and development. However, few neonatal intensive care units (NICUs) provide this early intervention. H-HOPE (Hospital to Home: Optimizing the Preterm Infant?s Environment) has established efficacy, and has a standardized protocol, making it ready for widespread implementation. The infant-directed component of H-HOPE provides Auditory (voice), Tactile (moderate touch massage), Visual (eye to eye), and Vestibular (rocking) stimulation starting when infants are ready for social interaction. The parent-directed component of H-HOPE includes participatory guidance and support to help parents engage with their infants in the NICU and the transition to home. In our NIH-funded research, H-HOPE improved growth, developmental maturity and mother-infant interaction, and reduced initial hospitalization costs and acute care visits through 6-weeks corrected age. This research tests whether H- HOPE can be implemented and sustained in five diverse NICUs, using a Type 3 Hybrid design to evaluate both implementation processes and effectiveness. The specific aims are to: 1) Identify the degree of implementation success; 2) Evaluate the effectiveness of H-HOPE for infants, hospital costs from H-HOPE enrollment until discharge, and parents, compared to a pre-implementation comparison cohort; and 3) Determine influences (facilitators and barriers) associated with implementation success and H-HOPE effectiveness, guided by the Consolidated Framework for Implementation Research (CFIR). An incomplete stepped-wedge design guides staggered roll-out for five clinical sites. Each NICU completes the CFIR implementation steps (Planning and Engaging, Executing, and Reflecting and Evaluating), followed by 6 months of Sustaining. For Aim 1, degree of implementation success is determined every two months as Sustainability (still offering H-HOPE), Reach (% of eligible parent/infant dyads receiving H-HOPE) and Degree of Implementation (mean H-HOPE services received per parent-infant unit) (primary implementation outcomes). For Aim 2, effectiveness is analyzed using generalized linear mixed models for infant, cost, and parent outcomes (primary outcomes: infant growth at discharge and acute care visits from discharge to 6- weeks corrected age). Propensity score analysis is used to make the pre- and post-implementation comparable. For Aim 3, we use mixed methods analyses to identify influences from H-HOPE records and interviews that are associated with implementation success and effectiveness at each site and across sites. This is the first time implementation in a NICU is guided by the evidence-based CFIR framework, and results will make a major contribution to implementation science. This study will produce an evidence-based implementation strategy and Toolkit to disseminate nationwide. Widespread H-HOPE implementation will make a significant change in clinical practice and improve preterm infant health and health care costs.